In the electronics industry, a continuing objective is to further and further reduce the size of electronic devices while simultaneously increasing performance and speed. Cellular telephones, personal data devices, notebook computers, camcorders, and digital cameras are but a few of the consumer products that require and benefit from this ongoing miniaturization of sophisticated electronics.
Integrated circuit (“IC”) assemblies for such complex electronic systems typically have a large number of interconnected IC chips. The IC chips, commonly called dies, are usually made from a semiconductor material such as silicon or gallium arsenide. Photolithographic techniques are used to form the various semiconductor devices in multiple layers on the dies.
Dies are encapsulated in a molded plastic package that has connectors or leads on the exterior of the package that function as input/output terminals for the die inside the package. The package includes an interposer and a die mounted on the top surface of the interposer.
The interposer may be comprised of a flexible resin tape, a rigid fiber-glass/copper sheet laminate, a co-fired ceramic coupon, a flexible metal lead frame, a ball grid array substrate or other well-known types of interposers in the semiconductor industry, depending on the particular type of semiconductor package being used.
The die is conventionally mounted to the top surface of the interposer with, for example, a layer of an adhesive or an adhesive film, and then electrically connected to the interposer by a number of fine, conductive wires, typically gold (Au) or aluminum (Al), that electrically connect the die to the interposer. The wires are attached to the die at the bonding pads of the die, which are located around the periphery of the die.
After one or more dies are wire bonded to the interposer, the dies, the interposer, and conductive wires are encapsulated in a mold material, such as plastic or epoxy, or in a multi-part housing made of plastic, ceramic, or metal. The encapsulation protects the interposer, the fine conductive wires, and the die from physical, electrical, moisture, and/or chemical damage.
Because of their fineness, wire sweep of the fine conductive wires is a constant problem during the encapsulation of a semiconductor die. The high viscosity of the encapsulation material in its liquid state during the encapsulation process drags the wires along the flow path of the material, causing the wires to bend away from their original upright positions. Wire sweep poses a reliability risk to the functionality of the semiconductor device. Wires that are swept may come in contact with each other causing shorts in the device. Wires that are swept may also touch the surface of the semiconductor die, which would cause shorts between different components on the die. Therefore, it is always desirable to keep the wire sweep level to a minimum to protect the functional integrity of the semiconductor device.
Certain factors contribute to the overall difficulty in limiting the wire sweep. As stated previously, flowing molding material exerts a drag force on the wires. If this force exceeds the strength of the wires or of the bonds, then the wires will bend. Longer wires tend to bend more easily than shorter wires; therefore, it is desirable to keep the wire lengths as short as possible. However, it is not always possible to keep the wire lengths short.
Another factor that contributes to the difficulty of controlling wire sweep is the proximity of the wires to each other. The closer the wires are together, the harder it is to reduce the possibility of wires coming into contact with each other. Miniaturization of circuit patterns on semiconductor dies results in wires being located closer together. Moreover, die designers are putting more components on a single die to expand its functions. Expanded functionality of each die results in more wires. More wires and smaller die circuit geometry require that the wires be much closer together, making wire sweep control far more difficult.
Thus, a need still remains to effectively control wire sweep. In view of the ever-increasing need to save costs and improve efficiencies, it is more and more critical that answers be found to this problem.
Solutions to this problem have been long sought but prior developments have not taught or suggested any and thus, answers to these phenomena have eluded those skilled in the art.